Air conditioning systems are currently commonplace in homes, office buildings and a variety of vehicles including, for example, automobiles. Over time, the refrigerant included in these systems becomes depleted and/or contaminated. As such, in order to maintain the overall efficiency and efficacy of an air conditioning system, the refrigerant included therein is periodically replaced or recharged.
Portable carts, also known as recover, recycle, recharge (“RRR”) refrigerant service carts or air conditioning service (“ACS”) units, are used in connection with servicing refrigeration circuits, such as the air conditioning unit of a vehicle. The portable machines include service hoses coupled to the refrigeration circuit to be serviced. A vacuum pump and compressor operate to recover refrigerant from the vehicle's air conditioning unit, flush the refrigerant, and subsequently recharge the system from a supply of either recovered refrigerant and/or new refrigerant from a refrigerant tank.
Currently available processes for recharging air conditioning systems typically include connecting the recharging unit to an air conditioning (“A/C”) system and transferring the refrigerant from a refrigerant tank of the recharging unit to the A/C system. A/C systems in automotive applications continue to get smaller in order to reduce the amount of refrigerant needed for efficient operation. The accuracy at which the A/C system is refilled is increasingly important in smaller A/C systems. Current industry standards for A/C service require a refill accuracy of +/−15 grams, but even tighter tolerances are desirable.
When the temperatures of the ACS machine and the system being charged are equal to ambient temperature, accurate charging is much easier. However, when temperatures vary, the refrigerant will migrate to the coldest area. For example, when charging a vehicle that is hot, the refrigerant will condense in the service hoses rather than traveling into the refrigerant system. In current ACS units, the amount of refrigerant remaining in the service hoses or fittings is difficult to accurately determine. Therefore, the refrigerant trapped in the service hoses is not accurately accounted for in the determination of the amount of refrigerant charged into the A/C system.
Some previous ACS units address the problem by performing a dynamic hose compensation based on temperature differentials between the refrigerant temperature and the ambient temperature. The ambient temperature, however, may not be a good approximation for the A/C system temperature when the vehicle in which the A/C system has been running or has been parked at a location that is different from where the ambient temperature is recorded. As a result, the known dynamic hose compensation does not accurately account for the temperature of the A/C system.
Additionally, the actual temperature of the A/C system is difficult to determine since the A/C system typically does not have temperature sensors to measure the system temperature. Furthermore, even if the temperature were determined at a location of the A/C system, some components in the A/C system often have differing temperatures due to proximity to components within the vehicle that transfer heat to the components of the A/C system or due to the A/C system being previously active, and therefore generating colder areas within the system.
In view of the above issues, improvements in determining the temperature in an A/C system to increase the precision of recharging the A/C system are desirable.